Immobilization devices such as a cast, a splint, a brace (orthosis) and stiffening apparatuses are used to impart a desired position to a portion of the body or to immobilize the supported portion relative to other parts of the body. Traditionally, plaster casting materials have been used because they are very low cost. However, plaster casting materials are heavy and cannot be cleaned or easily removed.
Recently, plaster casting materials have been replaced by synthetic casting materials which are lighter in weight and can be cleaned but have a rough exterior surface and are still relatively heavy and bulky. These materials are irritating to sensitive skin areas such as to facial skin.
Thermoplastic materials have been introduced for forming casts and braces and immobilization devices such as used in radiation therapy. Thermoplastic materials with high melting point preclude the possibility of moulding directly on a patient's skin as severe burns would result. These materials require the use of positive casts of the targeted part, to allow moulding and the use of large ovens for softening the sheets. The construction of positive casts is a particularly laborious and time consuming process.
These thermoplastic materials can be produced in extruded sheets which, when brought to a melt point temperature of 50° C. to 100° C., can be molded and manipulated to conform to and shape around a body part, such as a limb, and then allowed to cool to hardness. These materials can also be reheated, brought back to their original shape and then remolded into a different shape. Compared to other casting materials, the thermoplastic materials provide many advantages including simplicity of use and ease of cleaning. However, to be able to mold the material a temperature is required above the temperature which a sensitive skin such as facial skin can endure without damage.
Patients being treated by radiotherapy for a tumorous growth are typically required to receive radiation doses at regular intervals, whereby each dose should be precisely directed to the same location of the body. This necessitates immobilization materials and devices that are adapted to the shape of the body portion being treated.
However, a problem associated with the above-mentioned materials and devices made of thermoplastic material are that they lack flexibility. Another problem is that they are relatively heavy. Moreover, most materials are opaque, hence non-transparent. As a consequence, they do not permit observing the skin covered by it, nor do they permit adjusting the positioning of the material using markers present on one or both of the immobilization device and the covered body part.
The material for the manufacturing of casts for immobilization devices is preferably molded directly to the body part that needs to be immobilized prior to receiving radiotherapy. However, most casts are standardized so that there is some space between the body part in need of immobilization and the cast used thereto. This is problematic to accurately and quickly align the radiation source with the location of the tumor. This is especially problematic in the treatment of brain tumors where misalignment of the beam of radiation may cause brain damage.
A wide variety of plastic materials is known in the art for fixation or immobilization devices. Amongst those plastic materials, only a limited number have a sufficient formability and elasticity in the molten state at a temperature which can be supported by the body, to permit direct molding on a patient's body. Direct molding to the patient's body is important, as it permits adapting the size and shape of the immobilization device directly to each individual patient, in the position in which the body part is to be immobilized.
Moreover, most materials are not suitable for application to skin, especially not to soft skin such as facial skin. In addition, thermoplastic materials for immobilization devices or assemblies are quite rigid and hard upon crystallization when cooling down from the melting temperature. Consequently, the immobilization devices produced from these thermoplastic materials easily break in case of hard handling or after falling, which is a serious disadvantage.
There is thus a need for casting materials with improved properties. The invention therefor aims to provide a thermoplastic composition for forming a cast, resultant casts, and methods related thereto, that provide a solution to at least one of the problems previously mentioned.